Background
Carbon dioxide is the primary greenhouse gas driving global warming, and the burial of organic carbon in the ocean serves as a major natural mechanism for long-term CO2 sequestration. Mercury, a globally dispersed pollutant capable of long-range transport, poses a serious threat to human health and ecosystems. The Southern Ocean, a critical region in global carbon cycling and climate change, plays a significant role in sequestering both carbon dioxide and mercury, with its sediments considered a major sink for these substances. However, due to its remote location, in situ observations have long posed significant challenges for researchers. Furthermore, the impact of climate change on this sequestration process remains unclear. This raises a compelling question: will the Southern Ocean provide positive or negative climate feedback in the face of future warming? And what implications will this have for the fate of mercury?
Key Findings
We focused on the Ross Sea because it represents a typical ice-shelf sea in West Antarctica. We analyzed 20 sediment cores from the Ross Embayment and its extended open ocean, and the results reveal that the burial fluxes of organic carbon and mercury are highest in the near-ice-shelf zone, exhibiting a significant spatial decline towards the open ocean. Marine primary production is the primary source of organic carbon in the sediments, while external organic carbon inputs from glacial melt and surface erosion—including vegetation, soil, and the feces and fur of penguins and seals—provide additional contributions to the near-ice-shelf region. Atmospheric deposition, on the other hand, is identified as the dominant pathway for mercury input into the sediments of the study area. Glacial and terrestrial inputs shape the spatial patterns of organic carbon burial in the Ross Sea and capture substantial amounts of mercury from atmospheric deposition that settle into the marine and terrestrial ecosystems, thereby significantly enhancing the sediment’s capacity for mercury burial (Figure 1).
Furthermore, we found that the retreat of the Ross Sea Ice Shelf due to Holocene warming boosted primary production and released significant amounts of ancient carbon stored in the ice into the seawater (Figure 1). However, most of this organic carbon was remineralized into CO2, potentially turning the Ross Sea into an organic carbon reactor and exacerbating climate fluctuations. In contrast, warming has increased mercury burial by 3-8 times, decoupling it from the historical trend of organic carbon burial and significantly raising the risk of mercury pollution in the Ross Sea. This implies that climate warming could weaken the Ross Sea’s carbon sequestration capacity, potentially creating a positive feedback loop that exacerbates climate change, while simultaneously amplifying the ecological impacts of mercury in the Ross Sea.
Figure 1. Physical and biogeochemical processes affecting the transport and fate of organic carbon and mercury on the Antarctic continental shelf and open Southern Ocean. a. The Holocene. b. In present.
Behind the Research
This study underscores the vital role of international collaboration in Antarctic research, bringing together experts from diverse fields and nations to highlight the significance of multidisciplinary approaches in executing such endeavors. Although the core collaborators consisted of 12 researchers from six Chinese and U.S. institutions, the contributions of indirect participants far exceeded this number, including scientists and crew members from research expeditions, technicians in terrestrial laboratories, and logistical support teams. The journey from sample collection to lab analysis spanned years, marked by an intricate international division of labor.
For instance, a critical sediment core sample faced delays in international shipping, prompting labs across three nations to conduct a “relay-style” segmented analysis, while during the COVID-19, scientists achieved seamless data integration through 24-hour cross-time-zone virtual collaboration. The research employed nearly all mainstream biogeochemical analytical techniques—made possible by the team’s interdisciplinary expertise spanning geology, biology, marine chemistry, and atmospheric sciences. These lesser-known narratives, like the bedrock beneath Antarctica’s ice sheets, silently underpinned the groundbreaking discoveries published in the journal Nature Communications.
Implications for the Future
The burial of carbon and mercury in marine sediments plays a critical role in regulating the residence time of CO2 and mercury in the atmosphere and ocean, thereby influencing climate change and ecosystem health. The decoupling of the environmental fates of mercury and organic carbon highlights how climate warming affects their burial processes in distinct ways, potentially leading to feedback mechanisms that exacerbate global warming and amplify mercury pollution in the remote and pristine Antarctic region.
Our research underscores the urgent need for the international community to recalibrate expectations regarding the Southern Ocean’s capacity to buffer global warming, while also highlighting the growing threat of toxic mercury enrichment in the region due to rising temperatures. Reducing greenhouse gas emissions and anthropogenic mercury release remains the most effective strategy to mitigate these feedback mechanisms.
Call to Action
Given the vast spatial scale and complex system interactions of Antarctica, polar research demands extensive international collaboration, as no single nation or institution can adequately cover the multifaceted dynamics of this critical region. We hope nations worldwide will foster collaboration, as such partnerships inject new momentum into building a more inclusive and enduring framework for polar governance and scientific cooperation.
This study was funded by the National Natural Science Foundation of China (42476127 and 41821005), Fundamental Research Funds for the Central Universities (7100604309), China Postdoctoral Science Foundation (2022M720005), Beijing Natural Science Foundation (8244068), High-Performance Computing Platform of Peking University, and Peking University-BHP Carbon and Climate Wei-Ming PhD Scholars (WM202409).